This invention generally relates to ink jet printer apparatus and methods and more particularly relates to a drop-on-demand ink jet printer capable of directional control of ink drop ejection, and method of assembling the printer.
An ink jet printer produces images on a receiver by ejecting ink droplets onto the receiver in an imagewise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
However, it is desirable to control the angle at which the droplet travels to the recording medium. For example, if any one of ink ejection nozzles is inoperable, such as due to clogging or manufacturing defect, it would be desirable to redirect droplets from operable nozzles to print at locations that would otherwise be printed by the inoperable nozzle. In addition, if each nozzle can print dots at a plurality of locations on the receiver, then fewer nozzles are needed, thereby reducing print head manufacturing costs.
In addition, it is desirable to control velocity at which the ink droplets strike the recording medium. Control of velocity in turn controls printing speed.
Ink jet printers may be either DOD (Drop-Qn-Demand) or xe2x80x9ccontinuousxe2x80x9d ink jet printers. In this regard, in the case of DOD ink jet printers, at every orifice a pressurization actuator is used to produce the ink jet droplet. Either one of two types of actuators may be used. These two types of actuators are heat actuators and piezoelectric actuators.
A DOD ink jet printer having a heat actuator is disclosed in Great Britain Pat. No. 2,007,162, which issued to Endo et al. in 1979. In such a printer, a heater placed at a convenient location heats the ink and a quantity of the ink will phase change into a gaseous bubble and raise the internal ink pressure sufficiently for an ink droplet to be expelled to the recording medium. However, the Endo et al. patent does not disclose a technique for directional control of the ink droplet ejected from the printer. More specifically, the Endo et al. patent does not disclose a technique to redirect the ink droplets to a plurality of printing locations on the recording medium. In addition, the Endo et al. patent does not appear to disclose a technique for controlling velocity of the ink droplet.
A DOD ink jet printer combining a pressurized reservoir and a heat-assisted drop ejection mechanism is disclosed in U.S. Pat. No. 4,275,290, which issued to Cielo et al. According to the Cielo et al. patent, a liquid ink printing system supplies ink to a reservoir at a predetermined pressure and the ink is retained in orifices by surface tension until the surface tension is reduced by heat from an electrically energized resistive heater, which causes ink to issue from the orifice and to thereby contact a paper receiver. However, the Cielo et al. patent does not disclose a technique for directional control of the ink drop ejected from the printer. More specifically, the Endo et al. patent does not disclose a technique to redirect the ink droplets to a plurality of printing locations on the recording medium. In addition, the Cielo et al. patent does not appear to disclose a technique for controlling velocity of the ink droplet.
A DOD ink jet printer having a piezoelectric actuator is disclosed in U.S. Pat. No. 3,946,398, which issued to Kyser et al. in 1970. In this type of printer, a piezoelectric material is used, which piezoelectric material possesses piezoelectric properties such that an applied electric field produces a mechanical stress in the material to decrease ink channel volume and thereby eject an ink droplet. However, the Kyser et al. patent does not disclose a technique for directional control of the ink drop ejected from the printer. More specifically, the Kyser et al. patent does not disclose a technique to redirect the ink droplets to a plurality of printing locations on the recording medium. In addition, the Kyser et al. patent does not appear to disclose a technique for controlling velocity of the ink droplet.
A xe2x80x9ccontinuousxe2x80x9d ink jet printer is disclosed in U.S. Pat. No. 4,631,550 issued Dec. 23, 1986 to Michael J. Piatt, et al. and assigned to the assignee of the present invention. Such a continuous ink jet printer utilizes electrostatic charging tunnels that are placed close to where ink droplets are being ejected in the form of a stream. Selected ones of the droplets are electrically charged by the charging tunnels. The charged droplets are deflected downstream by the presence of deflector plates that have a predetermined electric potential difference between them. A gutter may be used to intercept the charged droplets, while the uncharged droplets are free to strike the receiver. However, the Piatt et al. patent does not disclose a technique for directional control of the ink drop ejected from a DOD printer. More specifically, the Kyser et al. patent does not disclose a technique to redirect the ink droplets ejected by a DOD printer to a plurality of printing locations on the recording medium. In addition, the Piatt et al. patent does not appear to disclose a technique for controlling velocity of the ink droplet.
However, attempts have been made to provide ink jet printers having ink ejection nozzles capable of placing ink droplets at different locations on a scan line. For example, a continuous ink jet printer having means for correcting droplet trajectories to account for variations in droplet xe2x80x9cthrow distancexe2x80x9d to improve droplet placement accuracy is disclosed in U.S. Pat. No. 4,540,990 issued Sep. 10, 1995 to Peter A. Crean. According to the Crean patent, distance sensing sensors periodically produce signals representative of the actual throw distance of the droplets and compare the signals indicative of the actual throw distance to a signal representative of the distance from the nozzles to a predetermined printing plane. The comparison signals are sent to a printer controller which adjusts the droplet trajectories in response thereto to correct the placement errors that would be caused by variations in the throw distance produced, for example, by wrinkles in the recording medium or dimensional tolerance variations in the recording medium transport system. Deflection of the droplets is obtained by varying deflection voltage of deflection electrodes that charge the droplets. However, the Crean patent does not disclose a technique for variable directional control of the ink drop ejected from a DOD ink jet printer because the Crean device is a continuous ink jet printer rather than a DOD ink jet printer. Also, the Crean patent does not disclose a technique other than use of a deflection voltage for directional control of the ink drop. Moreover, the Crean patent does not appear to disclose a technique for controlling velocity of the ink droplet.
Although each of the devices mentioned hereinabove is useful for its intended purpose, none of the DOD ink jet printing devices provides directional control of ink droplet ejection and none of the continuous ink jet printing devices uses a technique other than deflection voltage for directional control of the ink droplet. Moreover, none of the devices mentioned hereinabove controls velocity of the ink droplet.
Therefore, there has been a long-felt need to provide a drop-on-demand ink jet printer capable of directional control of ink drop ejection and method of assembling the printer.
An object of the present invention is to provide a drop-on-demand ink jet printer capable of directional control of ink drop ejection, so that any one of a plurality of ink ejection nozzles belonging to the printer prints at a plurality of locations on a recording medium.
With the above object in view, the present invention resides in a drop-on-demand ink jet printer capable of directional control of ink drop ejection, comprising a print head body having an ink ejection orifice adapted to poise an ink meniscus thereat about a center axis passing through the orifice; and a deflector coupled to the print head body and adapted to be in communication with the poised meniscus for lowering surface tension of a region of the poised meniscus, so that the poised meniscus deflects away from the region of lower surface tension and away from the center axis to define a deflected meniscus, whereby an ink drop separated from the deflected meniscus travels at an angle with respect to the center axis.
According to an exemplary embodiment of the present invention, the printer comprises a print head body having a plurality of elongate ink channels therein, each channel terminating in a generally circular ink ejection orifice. Each orifice is adapted to poise an ink meniscus thereat symmetrically about a center axis normal to the orifice. A plurality of arcuate-shaped heater segments are connected to the print head body and are symmetrically arranged in an annular ring surrounding each orifice. The heater segments are adapted to be in heat transfer communication with the poised meniscus and are capable of being energized for lowering surface tension of a predetermined side region of any one of the poised menisci. When a selected one of the heater segments is energized, a region of lower surface tension is created, such that the poised meniscus laterally deflects away from the side region of lower surface tension and away from the center axis to define a deflected meniscus. In this manner, an ink drop that is separated from the deflected meniscus travels along a trajectory at a predetermined angle with respect to the center axis. The angle is variable depending on the extent to which the heater segments are energized.
A pressurizer is connected to the print head body and is in communication with each of the channels for pressurizing the channels to form the poised menisci and thereafter to separate the ink drop from the deflected meniscus. In this regard, the pressurizer may be a plurality of deflectable piezoelectric transducers in communication with respective ones of the plurality of channels, the piezoelectric transducers being adapted to deflect into the channels while electrically stimulated for reducing volume of the channels so that the channels pressurize. Alternatively, the pressurizer may be a plurality of displaceable flexible membranes in communication with respective ones of the plurality of channels, the flexible membranes adapted to flex into the channels while pressurized for reducing volume of the channels so that the channels pressurize. On the other hand, the pressurizer may be a plurality of movable pistons in communication with respective ones of the plurality of channels, the pistons adapted to move into the channels for reducing volume of the channels so that the channels pressurize. Moreover, the pressurizer is controlled such that the pressurizer separates the ink drop at a predetermined velocity.
A feature of the present invention is the provision of a plurality of arcuate-shaped heater segments to laterally deflect the poised meniscus, so that an ink drop separated from the deflected meniscus travels along a trajectory at a predetermined variable angle.
Another feature of the present invention is the provision of a pressurizer in communication with each of the channels for pressurizing the channels to form the poised menisci and thereafter to separate the ink drop from the deflected meniscus, the pressurizer also being capable of controlling velocity of the ink drop.
An advantage of the present invention is that, if any one of the ejection orifices is inoperable, such as due to clogging or manufacturing defect, ink drops are redirected from the operable orifice to print at locations that would otherwise be printed by the inoperable orifice.
Another advantage of the present invention is that use thereof reduces print head manufacturing costs.
Yet another advantage of the present invention is that printing speed is variable depending on the particular needs of the print job.
These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there are shown and described illustrative embodiments of the invention.